Avian malaria-mediated population decline of a widespread iconic bird species.

Daria Dadam,J Marcus Rowcliffe,Andrew A Cunningham,Robert A Robinson,Anabel Clements,Malcolm Bennett,Will J Peach

doi:10.1098/rsos.182197

Abstract

Parasites have the capacity to affect animal populations by modifying host survival, and it is increasingly recognized that infectious disease can negatively impact biodiversity. Populations of the house sparrow (Passer domesticus) have declined in many European towns and cities, but the causes of these declines remain unclear. We investigated associations between parasite infection and house sparrow demography across suburban London where sparrow abundance has declined by 71% since 1995. Plasmodium relictum infection was found at higher prevalences (averaging 74%) in suburban London house sparrows than previously recorded in any wild bird population in Northern Europe. Survival rates of juvenile and adult sparrows and population growth rate were negatively related to Plasmodium relictum infection intensity. Other parasites were much less prevalent and exhibited no relationship with sparrow survival and no negative relationship with population growth. Low rates of co-infection suggested sparrows were not immunocompromised. Our findings indicate that P. relictum infection may be influencing house sparrow population dynamics in suburban areas. The demographic sensitivity of the house sparrow to P. relictum infection in London might reflect a recent increase in exposure to this parasite.

Highlights

Parasites have the capacity to affect animal populations by modifying host survival and/or reproductive success [1]
We investigated associations between parasite infection and house sparrow demography across suburban London where sparrow abundance has declined by 71% since 1995
Our findings indicate that P. relictum infection may be influencing house sparrow population dynamics in suburban areas

Summary

Introduction

Parasites have the capacity to affect animal populations by modifying host survival and/or reproductive success [1]. Breeding success is not a factor in the sparrow decline in the UK [17,18], whereas decreased overwinter survival [19], of juveniles [20], has been identified as driving this population decline. A study in Leicester (UK) found a lower fledging rate when the diet of nestlings contained a high percentage of vegetable matter compared to invertebrates [17] These results informed a large-scale supplementary feeding experiment in London, which showed that, while mealworm supplementation increased fledging success, it did not enhance recruitment of more juveniles into the breeding population [18]. Several hypotheses have been proposed to explain sparrow population declines in the urban/suburban environment, no conclusive cause has yet been identified. As far as we are aware, parasitism has not been previously investigated as a potential cause of the declines; parasites are generally understudied as a potential cause of avian population declines [23]

Methods

Results

Discussion

Conclusion